(Not Applicable)
(Not Applicable)
The present invention relates generally to valve seals, and more particularly to a binary balance seal assembly for use in valves particularly suited for cryogenic service.
There is currently known in the prior art valves which include pressure balanced shafts and plugs that are displaced during normal operation of the valve. A balanced shaft or plug typically includes holes or apertures through its length to ensure that pressure forces are balanced on either side of the shaft or plug. This balancing of pressure forces significantly reduces the force required to actuate the valve, and more particularly the movement of the plug between its open and closed positions. These particular types of valves include a xe2x80x9cbalance sealxe2x80x9d which extends about and is engageable to the plug to prevent fluid from upstream pressure leaking downstream of the plug. The balanced plugs are typically located in a pipe or ducting system in order to control fluid flow by essentially blocking that flow to varying degrees. The plugs are themselves typically fabricated from sturdy blocks of metal and moved by rods into and out of the fluid flow.
Balance seals as known in the prior art are often formed to include a portion which is deformed or deflected when exposed to pressure such that the deflected or deformed portion moves into sealed engagement with the valve plug. As such, the balance seal is often fabricated from a soft material to provide the requisite level of flexion/deformability. However, a problem arises when the valve including the balanced plug is used in cryogenic service applications wherein the temperature of the fluid flowing through the valve is about xe2x88x9250xc2x0 Fahrenheit or below. In these extremely low temperature ranges, the material of the balance seal loses its softness/resiliency, and thus its ability to expand or deflect into sealed engagement with the outer surface of the valve plug, particularly at low pressures of about five PSI or less. As will be recognized, the insufficiency of the sealed engagement between the balance seal and the valve plug facilitates the undesirable leakage of upstream pressure to downstream of the plug. The present invention is adapted to overcome this deficiency by providing a binary balance seal assembly having particular utility for use in valves including balanced plugs intended for use in cryogenic service, and adapted to prevent the above-described leakage problem typically encountered with existing balance seals.
In accordance with the present invention, there is provided a binary balance seal assembly for use in a balanced pressure valve specifically suited for cryogenic service. The valve itself includes a valve housing and a generally cylindrical valve plug which is movable within the valve housing between an open position and a closed position. More particularly, the valve plug resides within an internal chamber which is at least partially defined by an interior surface of the valve housing. Such interior surface includes an annular ramped portion.
The seal assembly of the present invention comprises an annular, energized primary seal which is adapted to be retained within the valve housing. The primary seal defines a central opening which is sized to accommodate the valve plug, and an annular seal well which is separated from the central opening by a deformable seal leg. The primary seal is oriented within the valve housing such that the movement of the valve plug from its closed position toward its open position facilitates the application of pressure to the primary seal, and more particularly to the interior of the seal well defined thereby. The application of pressure to the seal well of the primary seal facilitates the expansion or deformation of the seal leg into sealed engagement with the outer surface of the valve plug.
In addition to the primary seal, the seal assembly includes an annular, non-energized secondary seal which is adapted to be retained within the valve plug. The secondary seal has a generally rectangular cross-sectional configuration, and is oriented within the valve plug so as to be brought into sealed engagement with the ramped section of the interior surface of the valve housing when the valve plug is moved to its closed position. When brought into sealed engagement with the ramped section of the interior surface, the secondary seal effectively prevents upstream fluid from leaking to downstream of the valve plug. The primary and secondary seals are preferably fabricated from the same material, and more particularly a virgin polytetrafluorethylene.
Further in accordance with the present invention, there is provided a balanced pressure valve having the above-described structural attributes, and including the above-described binary balance seal assembly comprising the primary and secondary seals.